Maintenance 5-10 X-2 Technical Service Manual
Publication No: 15-02047
5.4.5 PA and Filter Assembly
The PA output transistors can be replaced without removing the PCB from
the heatsink. Refer to paragraph 5.3.6.
Many of the components on the PCB are accessible once the PA assembly is
removed from the main frame. Do not remove the PCB from the heatsink
unless absolutely necessary.
To remove the PA PCB assembly:
1. Disconnect the ribbon connector P1 and the twin coaxial connector P2.
2. Remove the four retaining screws securing the rear panel to the main
frame (two at each end of rear panel).
3. Remove the six screws securing the PCB to the septum panel:
• one at each corner of the PCB (4 off)
• one close to Tx/Rx relay K7
• one longer screw (16 mm) located between output transistor V14
and the Driver Heatsink.
4. Carefully withdraw the PCB assembly from the main frame.
To remove the PCB from the heatsink:
1. Remove the PA assembly as detailed above.
2. Unsolder and remove the three capacitors C87 to C89 mounted
between the bases of the output transistors V18 and V19.
3. Unsolder the wires and solder lugs fitted to the antenna sockets.
4. If the PCB is to be changed, unsolder and remove the negative and
positive power leads from their mountings on the PCB.
5. Remove the four screws securing the output transistors V18 and V19.
6. Remove the remaining three screws securing the PCB to the heatsink.
Note: The 12mm long screw removed from the driver heatsink must
be returned to this position when re-assembling.
7. Lift the PCB from the heatsink taking care not to damage the
thermistor (R22) and transistor V16 recessed into the heatsink. Take
care not to lose the mica insulator fitted under transistor V17.
To install the PCB to the heatsink:
1. Clean the underside of the output transistors V18/V19
[E11]
and bias
transistor V17. Clean the mating surfaces on the heatsink. Recoat
these surfaces with new thermal compound (e.g. Jermyn Theraflow
A30). Refit the mica insulator (if previously removed) coated with
thermal compound. Check there is sufficient thermal compound in the
two holes that locate the thermistor R22
[F4]
and transistor V16
[G9]
.
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